Bring the water or stock to a boil.
Add lemongrass, galangal, and kaffir lime leaves. Boil for 5 minutes.
Add meat or seafood and cook until just done.
Stir in the chili paste.
Season with fish sauce and sugar.
Turn off the heat and add milk and lime juice.
Adjust the sour, salty, and spicy balance.
Garnish with coriander and serve.